Recently, in performing a fine processing on a substrate, a process of forming an irregular pattern on the substrate (for example, a semiconductor wafer) using a photolithography technique has been extensively used. As an example, a process of forming a resist pattern on the semiconductor wafer includes forming a resist film on a surface of the semiconductor wafer, exposing the resist film with a predetermined pattern, and reacting a developing solution with the exposed resist film for development.
Various developing techniques have so far been developed. As an example, there is a developing scheme in which a paddle (liquid collected portion) formed of a developing solution is formed on a stationary substrate. A nozzle having a long discharge hole is used in forming the paddle. The nozzle is moved from one end of the substrate to the other end thereof while discharging the developing solution through the discharge hole such that the developing solution is applied on the entire surface of the resist film formed on the substrate. This developing scheme will be referred to as a “stationary developing scheme” for the sake of simplicity.
Further, there is a developing scheme of supplying a developing solution onto a rotating substrate. A nozzle supplies a developing solution onto the substrate through a discharge hole while moving in a radial direction of the substrate. A liquid film of the developing solution is formed on the resist film by virtue of an action of a centrifugal force generated by the rotation of the substrate and a movement of a position to which the developing solution is supplied. Hereinafter, for the sake of simplicity, the developing scheme of supplying the developing solution onto the rotating substrate will be referred to as a “rotational developing scheme”.
In addition, there is a developing method classified as the rotational developing scheme. Specifically, in this method, a nozzle having a bottom surface disposed to face a wafer is used. In a state where a gap between the wafer being in rotation and the bottom surface of the nozzle disposed in a region including a rotational center of the wafer is liquid-tightly maintained, a liquid is supplied onto the wafer and spread outwardly by virtue of a centrifugal force.
The stationary developing scheme fails to occur through convection of the developing solution in the paddle formed of the developing solution so that the developing solution having a degraded reactivity with respect to the resist film tends to be held in-situ. This requires a relatively long period of time for a development process.
In the rotational developing scheme, the developing solution supplied onto the substrate flows on the substrate. In this case, since the developing solution flows on the substrate, the developing solution, while flowing, reacts with the resist film. Thus, a concentration of the developing solution is changed along a direction in which the developing solution flows. The change of the concentration us, due to the flow of the developing solution, a distribution (which is also called an “in-plane line width distribution”) of line width of the resist pattern (which is also called a critical dimension (CD), and hereinafter, a line width of the resist pattern will be simply referred to as a “line width”) in a surface of the substrate may become uneven.